High voltage VJFETs implemented using Silicon Carbide (SiC) and other wide-bandgap materials may replace Silicon MOSFETs, superjunction MOSFETs and Silicon IGBTs in high power conversion and motor control applications. Wide bandgap semiconductors have higher breakdown fields (Ec, measured in V/cm) that translate into thinner voltage supporting drift regions, for example 10 times thinner, with higher doping, for example, greater than 10 times higher doping. This may directly result in many orders of magnitude reduction in device resistance in the on-state compared to a Silicon device of the same voltage rating.
VJFETs may be switched at relatively high frequencies with low power losses because they are unipolar devices. This may allow for more compact power electronic circuits. The switching speed is dictated by the device capacitances. In hard-switched applications, similar to most inductive loads like motors, reduced gate-drain capacitance (Cgd) may be critical.
Since the SiC VJFET devices do not have a gate oxide, they do not suffer from the reliability and yield problems faced by MOS gated Silicon Carbide devices. Furthermore, since the VJFET usually has a bulk channel instead of an inversion layer, they may be fabricated with a lower on-resistance than a MOSFET of comparable voltage rating. The absence of the gate oxide allows for reliable operation at higher peak junction temperatures.
Since SiC and other wide-bandgap materials are expensive, device structures that help decrease the die size are useful to make the devices economical for widespread use. The VJFET structures in the prior art may be improved upon both in the on-resistance per unit area at a given voltage rating, as well as in reducing Cgd and enhancing switching speed. Structures may also be implemented to incorporate a built in PiN diode or JBS Schottky diode to accommodate circuits requiring bi-directional current flow. The disclosure is directed to these and other important needs.